Generally the objectives of both present and future research are concerned with a better understanding of physiological phenomena on a cellular and molecular level. In the past, considerable emphasis was placed on the study of catecholamines and other hormones at the biochemical level with the resulting eventual clarification of some aspects of the biological role of cyclic AMP. These efforts will be continued. Emphasis will be placed on understanding the mechanism of control of cyclic AMP levels in tissues and cells. These studies will include the purification and characterization of adenylate cyclase from various sources. The investigation also represents an expanded evaluation of a negative feedback mechanism for controlling cellular cyclic AMP levels.